Hydropneumatic accumulator

ABSTRACT

A hydraulic accumulator includes an accumulator housing ( 1 ) and a diaphragm ( 3 ) forming a displaceable partition element in the housing between a gas chamber ( 7 ) and a liquid chamber ( 5 ). The membrane has several annular regions ( 31, 33, 35, 37, 39 ), interconnected by annular weak points ( 61, 63, 65, 67, 69, 71 ). The annular regions ( 31, 33, 35, 37, 39 ), have protuberances ( 81, 83, 85, 87, 89 ) on the interior face of the membrane ( 3 ) facing away from the wall of the accumulator housing ( 1 ). The protuberances are at their thickest in the central region between adjacent weak points, thus increasing the wall thickness of the membrane ( 3 ), and are at least partially convex ( 91,93 ), tapering off to a respective flat form towards the weak points.

FIELD OF THE INVENTION

The present invention relates to a hydropneumatic accumulator with anaccumulator housing and a membrane. The membrane is located in thehousing and forms a movable separating element between a first chamber,especially a gas chamber, and a second chamber, especially a liquidchamber. Several annular areas of the membrane are interconnected byannular weak points acting as articulations. The annular areas haveelevations on the inner side of the membrane facing away from the wallof the accumulator housing.

BACKGROUND OF THE INVENTION

Hydropneumatic accumulators are known in a host of constructions andembodiments. One of the main tasks of hydropneumatic accumulators(accumulators) is to accommodate certain volumes of pressurized liquidof a hydraulic system and to return it if necessary to the system.

DE-A-41 31 790 discloses a bladder or membrane for an accumulatorcomprising an elastic material layer. The elastic material layer islaminated with a gas blocking layer. An elastic fastener is formed onthe inside surface of a peripheral edge piece of the elastic materiallayer so that it or the material layer can be pressed onto the housing,if the fastener is attached to the housing by a holding element. Themembrane is made W-shaped in cross section. The thickness of the elasticmaterial layer decreases in an interposed section and/or increases onthe curved reverse area of the material layer. The convex middle area ofthe W-shaped membrane is therefore reversed to the edge of the membrane.In the direction of the fastener into a concavely extending curvatureand in spite of the thickness increase of the membrane intended in thisarea for a plurality of load cycles, its edge tearing and consequentlyfailure of the accumulator cannot be precluded.

Conversely, in an accumulator disclosed in DE-A-40 18 318, the membraneis divided into zones which are articulated to one another to helpprevent uncontrolled unfolding of the membrane during its workingmovements and to achieve longer service lives. In this known approach,conversely, between the deflection points of the membrane in the form offilm hinges, the membrane is embossed in plate or strip form. Thisembossing can be unfavorable in the process of unwinding of themembrane, especially when the plate-shaped elevations abut one another.Thus, increased force application in the area of the film articulationsoccurs.

DE-A-1 675 349 discloses a hydropneumatic accumulator with anaccumulator housing and a membrane located therein. The membrane forms amovable separating element between a first chamber, especially a gaschamber, and a second chamber, especially a liquid chamber, and hasseveral annular areas interconnected by annular weak points which actlike articulations. The annular areas have elevations on the inner sideof the membrane facing away from the wall of the accumulator housing. Inthe central area between adjacent weak points, the elevations have thegreatest height which increases the wall thickness of the membrane, andhave a shape tapering off towards these weak points. Each elevation isconvex at least in partial areas. In the known approach, the elevationsform annular beads or ribs which project out of the plane of theseparating element in the direction of the inner side of the membrane.Their convex arches taper off steeply in both directions and pass inthis way into elongated annular wall areas of the separating membranewhen viewed in the lengthwise direction of the hydraulic accumulator.The elongated annular wall areas keep the elevations in the initialposition of the separating element at equal distances to one another.Due to the sharply delineated transitions between the bead-shaped orannular elevations and the weak points which are formed from parts ofthe separating element with the same wall thickness, kinks in themembrane are formed. The result is that when it moves overstresses canform locally and accordingly it can fail.

SUMMARY OF THE INVENTION

Objects of the present invention are to provide an accumulatorcharacterized by especially good operating behavior of the membrane sothat a long service life can be achieved, even during operation withhigh pressure ratios and high rates of pressure change.

In an accumulator of this type, these objects are achieved in thepresent invention by the elevations, at least in the area bordering theadjacent weak points, taper off to the tangential plane of the pertinentweak points. This tangential plane is tangential relative to thestretched shape of the membrane, to the weak points, at a flat anglewhich is less than 20°.

The shape of the present invention has the areas of the membrane whichtaper off flatly towards the articulations, and avoids the danger thatwhen the membrane folds of overly sharp kinks at the joints form, as inthe aforementioned, known generic accumulators. Thus the damaging notcheffect is prevented. Conversely, the articulated movements for the shapeof the present invention take place with a certain radius of curvature,by which the danger of local overstress of the membrane is prevented.Without overly enlarging the wall thickness of the membrane, thus,comparatively large pressure amplitudes and rates of pressure change areallowable.

DE-A-28 52 912 discloses an accumulator with a thick-walled separatingelement of rubber. The inner annular areas on the separating element areformed with bead-like elevations. The elevations are beads or ribs whichproject out of the plane of the separating element, without the beads orribs having to be separated from one another by weak points which act inthe manner of a film hinge. Moreover, the beads in the areas adjacent toone another have a steeply tapering shape so that a careful unwindingprocess cannot be achieved with this known membrane.

In one preferred embodiment of the accumulator of the present invention,the weak points have a concave shape. The membrane has an alternatingsequence of convex with concave areas. This arrangement yieldsespecially good bending and unrolling properties in the folding of themembrane. Preferably, the membrane, in its initial position along itsouter surface, has a permanent and essentially uniform curvature, andthe membrane is designed in the manner of a hemisphere in its initialposition.

Preferably, the angle between the area of the elevations adjoining thebordering weak points and the tangential plane which belongs to thepertinent weak points, relative to the stretched shape of the membrane,is less than or equal to 15°.

Especially good bending properties arise when the membrane forms foldsif the elevations in the area bordering the weak points have a concavearch and in the area adjacent to the greatest height of the elevation, aconvex arch. At least parts of the elevations however can also be formedby planar surfaces, which preferably taper off towards the adjacent weakpoints.

In a membrane with a circular cross section and with annular areasarranged concentrically to one another and bordered by weak points whichform circles, the annular areas or at least some of them can be dividedby weak points which run transversely to the circles. These weak pointspreferably extend radially relative to the circle cross section.

The present invention makes it advantageously possible to produce themembrane from a gas-tight monolayer plastic, for example from apolyamide, a polyamide blend, polyethylene terephthalate, polyethylenenaphthalate or polyvinylidene chloride.

Other objects, advantages and salient features of the present inventionwill become apparent from the following detailed description, which,taken in conjunction with the annexed drawings, discloses preferredembodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a side elevational view in section or an accumulator accordingto a first embodiment of the present invention;

FIG. 2 is an enlarged, highly schematically simplified, partial sideelevational view in section of the membrane of the accumulator of FIG.1, with the membrane in its stretched state;

FIG. 3 is a top plan view of the membrane of the first embodiment drawnon the scale corresponding to FIG. 1, and

FIG. 4 is a top plan view similar to that of FIG. 3, of a membraneaccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The accumulator shown in FIG. 1 is a so-called membrane accumulator witha separating element located in the housing 1 and being in the form of amembrane 3. The membrane 3 separates the interior of the housing 1 intoa first chamber, in this example a liquid chamber 5, and into a secondchamber, in this example a gas chamber 7. Both the liquid chamber 5 andthe gas chamber 7 each have a connection 9 and 11, respectively, bywhich the accumulator can be connected to the pipelines of a hydraulicsystem (not shown) and by way of which the gas pressure can be set,respectively. Comparable accumulators with the previously describedfeatures are state of the art. The accumulator is explained below onlyto the extent which is necessary for description of the presentinvention.

The housing 1 includes, when viewed in FIG. 1, a top housing shell 13and a bottom housing shell 15 which abut one another along a seam 17.Along this seam 17, the two shells 13 and 15 can be joined to oneanother by an electron beam welding process or laser welding to form thehousing 1.

Within the housing 1, the membrane 3, which is shown in FIGS. 1 and 2 inits stretched state, is held by a steel ring 19. Ring 19 has a heightthat covers the seam 17 within the housing 1 with an excess length. Onits side facing the gas chamber 7, the ring 19 has recesses in the formof notches 21. The notches are rectangular in cross section and arearranged around the ring 19 at the same or equal distances from oneanother. On its side facing the liquid chamber 5, the ring 19 has aperipheral annular groove 23 with a lower edge, on its side facing theinside wall of the housing viewed in the direction of looking at FIG. 1.Groove 23 forms a shoulder surface 25 as an abutment for the edge bead27 of the membrane 3. Edge bead 27 has a rectangular cross section. Thecross section of the edge bead 27 and the depth of the annular groove 23are such that the membrane, on the edge bead 27, is held gas-tight onthe inside wall of the housing, if the ring 19 is fixed in theaccumulator housing. This fixing takes place in the course of thewelding process carried out after seating the upper housing shell 13. Toweld the housing 1 on the seam 17, the ring 19 being welded tightly tothe housing 1.

Details of the configuration of the membrane 3 can be taken from FIGS. 1to 3. FIGS. 1 to 3 show membrane 3 having a round a shape in an overheadview and a somewhat hemispherical shape in a side view. As is bestillustrated in FIG. 2, the membrane 3 on its entire outer surface, asidefrom the end-side edge bead 27, has a smooth surface. On its inside, themembrane has contouring. In the embodiment shown in FIGS. 1 to 3 thecontouring divides the membrane 3 on its inside into concentric annularareas 31, 33, 35, 37 and 39. These annular areas each are borderedlaterally by weak points 61, 63, 65, 67, 69 and 71 in which the membrane3 has its smallest wall thickness. These weak points extend along theinside periphery of the membrane along circles 41, 43, 45, 47, 49 and51. In the annular areas 31, 33, 35, 37 and 39 between the weak points,flat, bead-like elevations 81, 83, 85, 87 and 89, (see FIG. 2) areprovided.

As is clear from FIG. 2, each elevation 81, 83, 85, 87 and 89 has itsgreatest height, corresponding to the greatest wall thickness of themembrane, in the central area between the respective bordering weakpoints 61, 63, 65, 67, 69 and 71. In this example, each elevations inthis central area has a convex arch 91. One concave area 93 whichextends up to each bordering weak point laterally adjoins the convexarch 91. The concave areas 93 extend tapering off flatly to therespectively assigned weak points. The flat angle a of incline relativeto the tangential plane of the membrane 3 in the stretched state, whichplane is tangential relative to the respective weak point, is preferablyon the order of 12°to 14°.

Based on this configuration with elevations 81, 83, 85, 87, 89 whichrise gently at the weak points 61, 63, 65, 67, 69, 71. The weak points,when folds form in the membrane 3 as a result of the working motion ofthe membrane 3, form articulations in the manner of film hinges on whichfolding of the membrane takes place in a controlled manner. As a resultof the configuration of the present invention, no sharp kinks areformed. Local overstress of the membrane material is prevented, and highoperating service life is achieved.

FIG. 4 shows a second embodiment in which the membrane 3, in addition tothe weak points extending along the circles 41, 43, 45, 47, 49, 51, isarticulated by radially (relative to the circular shape) running weakpoints 95. These radially running weak points 95 divide the bead-likeelevations located within the annular areas and having the greatestheight in the central area between the bordering weak points in exactlythe same manner as is shown in FIG. 2 for the first embodiment. Fromthese areas of greatest prominence, the elevations taper off in thecorresponding manner as in the example from FIG. 2 to the bordering weakpoints which they approach at a flat angle. Here, a concavely/convexlycurved arch can be provided in the corresponding manner, as in FIG. 2.The concave arched areas approach both the weak points along the circles41, 43, 45, 47, 49, 51 and also the radially running weak points 95.

Instead of the arched shape shown in the figures, there can be otherarched shapes or combined shapes composed of arched areas and planesurface areas. However, the approach to the respectively bordering weakpoints takes place at flat angles. In the embodiments according to FIG.4, additional weak points which extend transversely or radially to thecircles need not be provided in the number as shown in FIG. 4. Thesetransversely extending weak points need not extend beyond all theannular areas, and can extend other than in a star-shape or radially.The film hinges shown in FIGS. 3 and 4 as weak points are shown for thesake of simplicity as concentric circles with the same distance betweenone another. As is shown in FIG. 2, the distances however are different,especially increasing from the outside to the inside toward the membranecenter.

The material for the membrane 3 is preferably gastight monolayerplastics, for example polyamide, such as PA6, a polyarrude blend, forexample PA polyolefin, or polyethylene terephthalate or polyethylenenaphthalate or polyvinylidene chloride. Other types of materials can beprovided for producing the membrane. The radius of curvature for theconcave weak points is smaller than the radius of curvature for theconvex elevations. In this respect, they are less strongly curved thanthe adjacent weak points.

While various embodiments have been chosen to illustrate the invention,it will be understood by those skilled in the art that various changesand modifications can be made therein without departing from the scopeof the invention as defined in the appended claims.

1. A hydropneumatic accumulator, comprising: an accumulator housinghaving a wall, a gas chamber and a liquid chamber; and a membranelocated in said housing and separating said gas chamber from said liquidchamber, said membrane having multiple annular areas interconnected byannular weak points functioning as articulations, said annular areashaving elevations on an inner side of said membrane facing away fromsaid wall of said accumulator housing, said elevations having centralareas between the respective weak points with greatest heights thereofincreasing wall thicknesses of said membrane thereat and having at leastpartially convex shapes tapering flatly towards the respective weakpoints, border areas of said elevations adjacent said weak pointstapering at flat angles to tangential planes of said membrane at saidweak points in a stretched position of said membrane, said flat anglesbeing less than 20 degrees.
 2. A hydropneumatic accumulator according toclaim 1 wherein said weak points have concave shapes; and said membranehas an alternating sequence of said convex shapes and said concaveshapes.
 3. A hydropneumatic accumulator according to claim 1 whereinsaid membrane has an initial position in which an outer surface thereofhas a permanent and essentially uniform curvature.
 4. A hydropneumaticaccumulator according to claim 3 wherein said outer surface ishemispherical in shape.
 5. A hydropneumatic accumulator according toclaim 1 wherein said flat angles are not greater than 15 degrees.
 6. Ahydropneumatic accumulator according to claim 1 wherein said membranehas a circular cross section; said annular areas are concentric to oneanother and are bordered by the respective weak points, said weak pointsforming circles; and at least some of said annular areas are divided byweak points extending radially relative to said circles.
 7. Ahydropneumatic accumulator according to claim 1 wherein said membrane isformed of a gaslight monomer plastic.
 8. A hydropneumatic accumulatoraccording to claim 7 wherein said plastic is a polyamide.
 9. Ahydropneumatic accumulator according to claim 8 wherein said polyamideis PA6.
 10. A hydropneumatic accumulator according to claim 7 whereinsaid plastic is a polyamide blend.
 11. A hydropneumatic accumulatoraccording to claim 10 wherein said polyamide blend is PA polyolefin. 12.A hydropneumatic accumulator according to claim 7 wherein said plasticis polyethylene terephthalate, polyethylene naphthalate orpolyvinylidene chloride.